COMPUTER NETWORKS (“COMPUTING”)
Task 1(p.66)
Try to answer these questions.
I What is a LAN?
2 What is a WAN?
3 What is a distributed system?
Reading
Task 2 (p.66)
Before reading the text below match these words and phrases with their definitions.
1 protocol
a analyse the syntax of a string of input symbols
2 bulletin board
b a teleconferencing system allowing users to read messages left by
3 user interface
other users
c agreement governing the procedures used to exchange information
4 make a query
between co-operating computers
5 parse
d means of communication between human user and a computer system
6 synchronous
e taking place at exactly the same time as something else
f request a search
Task 3 (p.67)
Read quickly through the text below, then match each paragraph with the appropriate summary.
a Network uses, past and present
b How distributed systems work
c Networks and the future
d What networks are and how they operate
e The growth of networks, past and present
Computer networks
Computer networks link computers by communication lines and software protocols, allowing
data to be exchanged rapidly and reliably. Traditionally, networks have been split between wide
area networks (WANs) and local area networks (LANs). A WAN is a network connected over
long-distance telephone lines, and a LAN is a localized network usually in one building or a group
of buildings close together. The distinction, however, is becoming blurred. It is now possible to
connect up LANs remotely over telephone links so that they look as though they are a single LAN.
Originally, networks were used to provide terminal access to another computer and to
transfer files between computers. Today, networks carry e-mail, provide access to public databases
and bulletin boards, and are beginning to be used for distributed systems. Networks also allow
users in one locality to share expensive resources, such as printers and disk-systems.
Distributed computer systems are built using networked computers that co-operate to
perform tasks. In this environment each part of the networked system does what it is best at. The
high-quality bit-mapped graphics screen of a personal computer or workstation provides a good
user interface. The mainframe, on the other hand, can handle large numbers of queries and return
the results to the users. In a distributed environment, a user might use his PC to make a query
against a central database. The PC passes the query, written in a special language (e.g. Structured
Query Language - SQL), to the mainframe, which then parses the query, returning to the user only
the data requested. The user might then use his PC to draw graphs based on the data. By passing
back to the user’s PC only the specific information requested, network traffic is reduced. If the
1
whole file were transmitted, the PC would then have to perform the query itself, reducing the
efficiency of both network and PC.
In the 1980s, at least 100,000 LANs were set up in laboratories and offices around the world.
During the early part of this decade, synchronous orbit satellites lowered the price of long-distance
telephone calls, enabling computer data and television signals to be distributed more cheaply
around the world. Since then, fibre-optics cable has been installed on a large scale, enabling vast
amounts of data to be transmitted at a very high speed using light signals.
The impact of fibre optics will be considerably to reduce the price of network access. Global
communication and computer networks will become more and more a part of professional and
personal lives as the price of microcomputers and network access drops. At the same time,
distributed computer networks should improve our work.
Task 4 (p.68)
Read this summary of the text and fill in the gaps using the list of words.
Computer networks link computers locally or by external communication lines and software
1______, allowing data to be exchanged rapidly and reliably. The 2 _____ between local area and
wide area networks is, however, becoming unclear. Networks are being used to perform
increasingly diverse tasks, such as carrying e-mail, providing access to public databases, and for 3
_____. Networks also allow users in one locality to share resources.
Distributed systems use networked computers. PCs or 4_____ provide the user 5_____.
Mainframes process 6_____ and return the results to the users. A user at his PC might make a
query against a central database. The PC passes the query, written in a special language, to the
mainframe, which then 7_____ the query, returning to the user only the data requested. This
allows both the network and the individual PC to operate efficiently.
In the 1980s, at least 100,000 8______ were set up world-wide. As 9_____ orbit satellites
have lowered the price of long-distance telephone calls, data can be transmitted more cheaply. In
addition, 10 _____ cable has been installed on a large scale, enabling vast amounts of data to be
transmitted at a very high speed using light signals. This will considerably reduce the price of
network access, making global networks more and more a part of our professional and personal
lives. Networks should also improve our work 11_____ and technical abilities.
Distinction
Distributed systems
Environments
fibre-optic
LANs
parses
protocols
synchronous
queries
workstations
screen handling
Task 5 (p.68)
Look back in the text and find words that have a similar meaning to:
1 unclear
2 place
3 carry out
4 cost
5 world-wide
Task 6 (p.68)
Look back in the text and find words that have an opposite meaning to:
1 disparate 2 conflict 3 preventing
4 tiny
5 increase
NETWORK CONFIGURATIONS
Task 10(p.70-71)
2
PC
PC
File server
PC
PC
PC
PC
PC
Central computer
PC
PC
PC
PC
PC
A
PC
B
Computer
PC
Phone
PC
Exchange
PC
PC
PC
File server
PC
PC
Phone
PC
C
D
Star(p.71)
In the star configuration, the central computer performs all processing and control functions. All
access devices are linked directly to the central computer. The star configuration has two major
limitations. First of all, the remote devices are unable to communicate directly. Instead, they must
communicate via the central computer only. Secondly, the star network is very susceptible to
failure, either in the central computer or the transmission links.
Switched
The central switch, which could be a telephone exchange, is used to connect different devices on
the network directly. Once the link is established, the two devices communicate as though they
were directly linked without interference from any other device. At the end of the session, the
connection is closed, freeing capacity for other users and allowing access to other devices.
Multiple switches can be used to create alternative transmission routes.
Ring
Each device is attached to a network shaped as a continuous loop. Data proceeds in only one
direction and at a constant speed round the loop. Devices may send information only when they
are in control of the ‘token’. The token is a package of data which indicates which device has
control. The receiving device picks up the token, then clears it for another’s use once it has
received the message. Only one device may send data at any given moment, and each device must
be working for the network to function.
Bus/Ethernet
A bus network consists of one piece of cable terminated at each end to which
all devices are connected. In a bus-based network, each device is able to broadcast a message
when it has detected silence for a fixed period of time. All devices receive the broadcast and
determine from the content of the message whether it was intended for them. The only problem
3
occurs when two devices try to send at the same time. When a sending device detects another
transmission, it aborts its own.
Task 11 (p.72)
These are answers to questions about the text. Write the questions.
1 To connect different devices on the network directly.
2 No, it goes in only one direction round the loop.
3 No, only one device may send data at any given moment.
4 From the content of the message.
5 It cancels its own transmission.
Task 12 (p.72)
Which of the network configurations on page 71 does this flowchart refer to?
Listen
Anyone
else
sending?
No
No
Data to send?
Yes
Start sending
Yes
Am I
trying
to send?
No
No
Data for me?
Yes
Abort send
Yes
Receive data
Wait
Task 13 (p.72)
The columns below describe characteristics of the bus and ring configurations. Which column
refers to which configuration? How did you decide?
A
B
Varied time response
Calculable time response
Easy expansion
difficult reconfiguration
Fault-tolerant
Fault-intolerant
Simple
More complex
ECU
UNIT 27 LANs and WANs (p.127)
4
1 Warm-up
Try to answer these questions.
1. What is a computer network?
2. What are the benefits of connecting computers and peripherals in a network?
3 Reading (p.127)
Read the text and then match these technical terms with their definitions.
1 LAN
a) the hardware that emits and receives signals in a computer network architecture
2 network
b) a network contained in a relatively small area
3 nodes
c) the arrangement of nodes in a communication system (i.e.the distribution of
elements in a network)
4 protocol
d) a device that translates protocols between different types of networks (e.g. it can
link networks of PCs and Macs to mainframes and minicomputers)
5
e) a special unit of data which acts as a key on a Token Ring network; only the
transceiver machine in procession of this piece of software can transmit on the network
f) a set of rules that allows the exchange of information over a network
6 token
g) computer devices interconnected in a network.
7 gateway
Network configurations (p.128)
A data communications network is a group of devices (CPUs, printers, etc.) or ‘nodes’
interconnected by communications circuits so that users can share data, software programs and
hardware resources. There are two different elements in this kind of network: the physical structure
that links the equipment, and the software that allows communication.
The physical distribution of nodes and the interconnecting communication circuits is known as
network ‘topology’ or ‘architecture’. The software consists of the protocols, i.e. the rules which
determine the formats by which information may be exchanged between different systems. We
could say that cables and transceivers ( the architecture) allow computers to ‘hear’ one another,
while the software is the ‘language’ that they use to ‘talk’ to one another over the network.
As regards the cables, they consist essentially of the transceiver – the hardware that sends and
receives network signals. At present the most widely used transceivers are: Token Ring, Ethernet,
and LocalTalk. Token Ring is the most common method of connecting PCs and IBM mainframes.
Most Token Ring adapters transmit data at a speed of 16 megabits per second. With Ethernet, data is
transmitted at 10 Mbits/sec. Ethernet provides a very robust, trouble-free architecture with good
levels of performance. In this regard, Ethernet is the best solution for fast and intensive activity. It is
also recommended for electronic colour printing or three-dimensional CAD. LocalTalk transceivers
are the cheapest of all because they are included in each Apple Macintosh. However A LoalTalk
network is a bit slow, which is why most Macs come with additional circuitry for connecting to a
high-speed network.
As for protocols, these are rules which describe things like transmission speed and physical
interfaces. They also define functions such as printing and file sharing. The Token Ring protocol
avoids the possibility of collisions. To transmit data, a workstation needs a token, and as there is
only one token per network, holding one guarantees sole use of the network. With Ethernet there are
other options, of which TCP/IP (Transmission Control Protocol/Internet Protocol) is perhaps the
most useful since it allows different operating systems to communicate with each other. With regard
to LocalTalk networks, they use Apple Talk Protocols. The Macintosh operating system includes the
Apple Talk manager and a set of drivers that let the programs on different Macs exchange
information.
LANs can be interconnected by gateways. these devices help manage communications and
control traffic on large networks. They can translate protocols of different networks which means
5
that a LocalTalk network running an Apple Talk protocol can be connected to an Ethernet network
running TCO/IP.
5 WANs and worldwide communications (p.130)
Try to answer these questions.
1. What is WAN?
2. How can computers be linked up over a long distance?
3. What are the advantages of optical-fibre cables over telephone lines?
4. What is the function of communications satellites?
Now read the passage and find out if your answers were correct.
For long distance or worldwide communications, computers and LANs are usually
connected into a wide area network (WAN) to form a single, integrated network. Two good
examples of wide area networks are Internet and arpanet. They transfer data and e-mail for
university researchers and academics, commercial groups, military installations and ordinary
people.
Networks can be linked together by either telephone lines or fibre-optic cables. For
example, ISDN (Integrated Service Digital Network) is an international standard for transmitting
digital text, sound, voice and video data over telephone lines. On the other hand, FDDI (Fibre
distributed Data Interface) is an optical-fibre network. This new standard transmits data at great
sped – 100 megabits per second.
Modern telecommunications use fibre-optic cables because data can be transmitted at a
very high speed through the extremely wide bandwidth of glass fibres. The fibre system operates
by transmitting light pulses at high frequencies along the glass fibre. This offers considerable
advantages: (i) the cables require little physical space; (ii)they are safe because they don’t carry
electricity; (iii) they avoid electromagnetic interference.
Networks on different continents can also be connected via satellite. Computers are
connected by modem either to ordinary telephone wires or fibre-optic cables, which are linked to a
dish aerial. This aerial has a large concave reflector for the reception and sending of signals. Then,
when signals are received by the satellite, they are amplified and sent on to workstations in another
part of the world.
6
Word-play Task 15 (p.74)
Solve the crossword puzzle using the clues below.
1
2
3
4
5
6
7
8
9
10
Across
1 The means of communication between a human and a computer.
5 To load software on to a computer, ready for use.
7 To transmit a message to all nodes on a network.
9 and 3 down Usually found in one building or a group of buildings together.
10 This kind of network often uses a telephone exchange to connect different devices directly.
Down
2 Taking place at exactly the same time as something else.
3 See 9 across.
4 An _____ board may be inserted into a computer to give it added features.
6 The opposite of 9 across and 3 down.
8 The network configuration in which all devices are linked through the central computer.
Word-play
Task 15 (p.74)
Solve the crossword puzzle using the clues below.
1
2
3
4
5
6
7
8
9
10
Across
1 The means of communication between a human and a computer.
5 To load software on to a computer, ready for use.
7 To transmit a message to all nodes on a network.
9 and 3 down Usually found in one building or a group of buildings together.
10 This kind of network often uses a telephone exchange to connect different devices directly.
Down
2 Taking place at exactly the same time as something else.
3 See 9 across.
4 An _____ board may be inserted into a computer to give it added features.
6 The opposite of 9 across and 3 down.
8 The network configuration in which all devices are linked through the central computer.
7
Key (127)
1b 2c3g 4f 5a 6e 7d
1 A WAN is a wide area network. (For long-distance communications, small area networks are usually connected
into a WAN.)
2 Computers can be linked over long distances by telephone lines or fibre-optic cables. They are connected to the
wires by means of a modem.
3 Fibre-optic cables offer considerable advantages:
- they require little physical space
- they are safe because they don't carry electricity.
- they avoid electromagnetic interference.
- they transmit information at high speed.
4 Communications satellites receive and send signals on a transcontinental scale.
8
Test
Before reading the text below match these words and phrases with their definitions.
1. protocol
a analyse the syntax of a string of input symbols
2.
bulletin board
b a teleconferencing system allowing users to read messages left by other users
3.
user interface
c agreement governing the procedures used to exchange information between co4.
make a query
operating computers
5.
parse
d means of communication between human user and a computer system
6. synchronous
e taking place at exactly the same time as something else
f request a search
Computer networks
Computer networks link computers by communication lines and software protocols, allowing data to be
exchanged rapidly and reliably. Traditionally, networks have been split between wide area networks (WANs) and
local area networks (LANs). A WAN is a network connected over long-distance telephone lines, and a LAN is a
localized network usually in one building or a group of buildings close together. The distinction, however, is
becoming blurred. It is now possible to connect up LANs remotely over telephone links so that they look as though
they are a single LAN.
Originally, networks were used to provide terminal access to another computer and to transfer files between
computers. Today, networks carry e-mail, provide access to public databases and bulletin boards, and are beginning
to be used for distributed systems. Networks also allow users in one locality to share expensive resources, such as
printers and disk-systems.
Distributed computer systems are built using networked computers that co-operate to perform tasks. In this
environment each part of the networked system does what it is best at. The high-quality bit-mapped graphics screen
of a personal computer or workstation provides a good user interface. The mainframe, on the other hand, can handle
large numbers of queries and return the results to the users. In a distributed environment, a user might use his PC to
make a query against a central database. The PC passes the query, written in a special language (e.g. Structured
Query Language - SQL), to the mainframe, which then parses the query, returning to the user only the data
requested. The user might then use his PC to draw graphs based on the data. By passing back to the user’s PC only
the specific information requested, network traffic is reduced. If the whole file were transmitted, the PC would then
have to perform the query itself, reducing the efficiency of both network and PC.
In the 1980s, at least 100,000 LANs were set up in laboratories and offices around the world. During the early
part of this decade, synchronous orbit satellites lowered the price of long-distance telephone calls, enabling
computer data and television signals to be distributed more cheaply around the world. Since then, fibre-optics cable
has been installed on a large scale, enabling vast amounts of data to be transmitted at a very high speed using light
signals.
The impact of fibre optics will be considerably to reduce the price of network access. Global communication
and computer networks will become more and more a part of professional and personal lives as the price of
microcomputers and network access drops. At the same time, distributed computer networks should improve our
work.
Task 4 (p.68)
Read this summary of the text and fill in the gaps using the list of words.
Computer networks link computers locally or by external communication lines and software 1______,
allowing data to be exchanged rapidly and reliably. The 2 _____ between local area and wide area networks is,
however, becoming unclear. Networks are being used to perform increasingly diverse tasks, such as carrying e-mail,
providing access to public databases, and for 3 _____. Networks also allow users in one locality to share resources.
Distributed systems use networked computers. PCs or 4_____ provide the user 5_____. Mainframes process
6_____ and return the results to the users. A user at his PC might make a query against a central database. The PC
passes the query, written in a special language, to the mainframe, which then 7_____ the query, returning to the user
only the data requested. This allows both the network and the individual PC to operate efficiently.
In the 1980s, at least 100,000 8______ were set up world-wide. As 9_____ orbit satellites have lowered the
price of long-distance telephone calls, data can be transmitted more cheaply. In addition, 10 _____ cable has been
installed on a large scale, enabling vast amounts of data to be transmitted at a very high speed using light signals.
This will considerably reduce the price of network access, making global networks more and more a part of our
professional and personal lives. Networks should also improve our work 11_____ and technical abilities.
Distinction
Distributed systems
Environments
fibre-optic
LANs
parses
protocols
synchronous
queries
workstations
screen handling
9
Look back in the text and find words that have a similar meaning to:
1 unclear
2 place 3 carry out 4 cost 5 world-wide
Look back in the text and find words that have an opposite meaning to:
1 disparate 2 conflict 3 preventing 4 tiny 5 increase
Read the text and then match these technical terms with their definitions.
1 LAN
a) the hardware that emits and receives signals in a computer network architecture
2 network
b) a network contained in a relatively small area
3 nodes
c) the arrangement of nodes in a communication system (i.e.the distribution of elements in a
network)
4 protocol
d) a device that translates protocols between different types of networks (e.g. it can link
networks of PCs and Macs to mainframes and minicomputers)
5
e) a special unit of data which acts as a key on a Token Ring network; only the machine in
transceiver procession of this piece of software can transmit on the network
f) a set of rules that allows the exchange of information over a network
6 token
g) computer devices interconnected in a network.
7 gateway
Network configurations (p.128)
A data communications network is a group of devices (CPUs, printers, etc.) or ‘nodes’ interconnected by
communications circuits so that users can share data, software programs and hardware resources. There are two
different elements in this kind of network: the physical structure that links the equipment, and the software that
allows communication.
The physical distribution of nodes and the interconnecting communication circuits is known as network
‘topology’ or ‘architecture’. The software consists of the protocols, i.e. the rules which determine the formats by
which information may be exchanged between different systems. We could say that cables and transceivers ( the
architecture) allow computers to ‘hear’ one another, while the software is the ‘language’ that they use to ‘talk’ to
one another over the network.
As regards the cables, they consist essentially of the transceiver – the hardware that sends and receives
network signals. At present the most widely used transceivers are: Token Ring, Ethernet, and LocalTalk. Token
Ring is the most common method of connecting PCs and IBM mainframes. Most Token Ring adapters transmit
data at a speed of 16 megabits per second. With Ethernet, data is transmitted at 10 Mbits/sec. Ethernet provides a
very robust, trouble-free architecture with good levels of performance. In this regard, Ethernet is the best solution
for fast and intensive activity. It is also recommended for electronic colour printing or three-dimensional CAD.
LocalTalk transceivers are the cheapest of all because they are included in each Apple Macintosh. However A
LoalTalk network is a bit slow, which is why most Macs come with additional circuitry for connecting to a highspeed network.
As for protocols, these are rules which describe things like transmission speed and physical interfaces. They
also define functions such as printing and file sharing. The Token Ring protocol avoids the possibility of
collisions. To transmit data, a workstation needs a token, and as there is only one token per network, holding one
guarantees sole use of the network. With Ethernet there are other options, of which TCP/IP (Transmission Control
Protocol/Internet Protocol) is perhaps the most useful since it allows different operating systems to communicate
with each other. With regard to LocalTalk networks, they use Apple Talk Protocols. The Macintosh operating
system includes the Apple Talk manager and a set of drivers that let the programs on different Macs exchange
information.
LANs can be interconnected by gateways. these devices help manage communications and control traffic
on large networks. They can translate protocols of different networks which means that a LocalTalk network
running an Apple Talk protocol can be connected to an Ethernet network running TCO/IP.
10